1. Field of the Invention
The present invention relates to a method of chemically growing a thin film in a gas phase on a silicon semiconductor substrate. More particularly, the invention relates to a method of chemically growing a thin film in a gas phase on a silicon semiconductor substrate to form a thin film such as a silicon thin film or a silicon epitaxial single crystal thin film on the surface of the substrate by using a rotary gas phase thin film growth apparatus which rotates the silicon semiconductor substrate while feeding a material gas onto the upper surface of the substrate by causing the gas to flow downward from above.
2. Prior Art
A conventional method of chemically growing a thin film in a gas phase on a silicon semiconductor substrate will now be described with reference to FIG. 2 which is a diagram of a relationship between the effective component gas for film-forming, the thin film growth rate and the film-forming temperature.
In the manufacture of a semiconductor, a method of chemically growing a thin film in a gas phase (the CVD method) is generally used to form a thin film on a surface of a silicon semiconductor substrate. In such method of chemically growing a thin film in a gas phase, a material which contains a component of a thin film to be grown is fed such that a depositional growth of a thin film of a desired component is realized by a chemical contact reaction on a surface of a substrate on which the thin film is to be grown.
Further, an apparatus used to operate said method of chemically growing a thin film in a gas phase (the CVD method) is divided broadly into a vertical type apparatus which feeds a material gas onto the surface of a silicon semiconductor substrate from above and a horizontal type apparatus which feeds a material gas to the surface of the silicon semiconductor substrate from sideways.
Now, in case where said horizontal type apparatus is used, it is difficult to grow a silicon single crystal layer such as a silicon epitaxial single crystal thin film or the like uniformly on the surface of the silicon semiconductor substrate having a diameter of 200 mm or more. Moreover, the silicon semiconductor substrate having a diameter of 300 mm or more is nowadays in general use. Therefore, the vertical type apparatus is finding a wider application.
Particularly, in order to grow a thin film having uniform inside characteristics, a single wafer type rotary gas phase thin film growth apparatus which is able to rotate the silicon semiconductor substrate is generally adopted out of a variety of vertical type apparatuses.
In addition, as a material gas to grow such thin film, for example to grow a silicon thin film on the surface of the silicon semiconductor substrate, monosilane (SiH4), dichlorosilane (SiH2Cl2), trichlorosilane (SiHcl3), silicon tetrachloride (SiCl4) or the like is used as an effective component gas.
Said effective component gas is generally mixed, together with a very small amount of dopant (doping material such as B2H6), with a carrier gas such as hydrogen gas or the like to be fed into a reactor.
Further, in case where said single wafer type vertical rotary gas phase thin film growth apparatus is used to grow the thin film on the surface of the silicon semiconductor substrate by the CVD method, it is known that relationship between the film growth rate and the film-forming temperature of said respective effective component gases is as shown in FIG. 2.
Furthermore, the diagram shown in FIG. 2 is generally called Arrhenius plot, in which a transversal axis is representative of a reciprocal of the temperature whereas a vertical axis is representative of a logarithmically plotted film-forming rate.
It is clear from FIG. 2 that in a high temperature range, a gradient of growth rate is gentle in any effective component gas and a temperature dependency of the growth rate is low, where a film deposition reaction is subject to a material transfer rate.
On the other hand, in a low temperature range, the gradient of growth rate is steep and the temperature dependency of the growing rate is high; that is to say, the film deposition reaction is subject to a reaction rate in this temperature range (low temperature range).
It is clear from the fact mentioned above that the uniformity of the thin film is easily controllable in said high temperature range (material-transfer-rate-dependant area) than in said low temperature range (reaction-rate-dependant area). Therefore, it is general to grow a film (thin film-forming) in the high temperature range. To be more specific, film-forming is done at temperature range of 1000xc2x0 C. to 1200xc2x0 C.
By the way, FIG. 2, shows examples of use of the component gases such as monosilane, dichlorosilane, trichlorosilane and silicon tetrachloride that are effective component gases to grow into a silicon thin film on the silicon semiconductor substrate. Of these component gases, a substance having a larger number of chlorines in a molecule thereof has said material-transfer-rate-dependant area closer to the high temperature side. Therefore, conventionally, in a substance having a larger number of chlorines in its molecules, the CVD reaction thereof must be done at a higher temperature.
As a result, an edge dislocation called xe2x80x9cslipxe2x80x9d is apt to occur within the silicon semiconductor substrate or within the thin film during this heat treatment. Thus, said xe2x80x9cslipxe2x80x9d dislocation is principally caused by stress concentration due to heat distortion or the like. On the other hand, tensile power of the silicon semiconductor substrate decreases as the temperature rises. Therefore, more slip dislocations are observed as the heat treatment temperature (the film forming temperature) rises.
In addition, the silicon semiconductor substrate with a larger diameter is more likely to produce a warp or a deformation. And the warp or the deformation is produced even by a slightest ununiformity in heating or the like in a silicon semiconductor substrate having a diameter of as large as 300 mm or more.
As a result, by a local stress concentration, the slip dislocation occurs more frequently in the treatment at the film-growing temperature which has not been a problem in case where the diameter of the silicon semiconductor substrate is smaller. Recently, as the diameter of the silicon semiconductor substrate tends to be larger, such occurrence of the slip dislocation is becoming a serious problem.
It is an object of the present invention to provide a method of chemically growing a thin film in a gas phase which is able to grow a film in a low temperature range, restrain an occurrence of a slip dislocation of a silicon semiconductor substrate and obtain a thin film whose quality is more than or equal to the conventional thin film.
The present invention provides a method of chemically growing a thin film in a gas phase using a rotary gas phase thin film growing apparatus which feeds a material gas by causing the gas to flow downward from above onto a surface of a rotating silicon semiconductor substrate to grow a thin film thereon such that a thin film-growing reaction is done wherein monosilane gas is used as an effective component of the material gas to grow into a thin film, under a reduced pressure of from 2.7xc3x97102 to 6.7xc3x97103 Pa, with the number of rotations of said silicon semiconductor substrate being from 500 to 2000 minxe2x88x921 and the reaction temperature being from 600xc2x0 C. to 800xc2x0 C.
Here, it is desired that a silicon thin film growth rate of said thin film growing reaction is within a range of 0.01 to 0.5 xcexcm/min.
It is further, desired that composition of said material gas is monosilane gas from 0.5 to 20 mol %, a doping material from 0.1 to 50 ppb and the remainder is a carrier gas. Furthermore, it is desired that said carrier gas is hydrogen gas.
Further, it is desired that the downward flow rate of said material gas is from 0.01 to 0.15 L(litter)/cm2xc2x7min.
The present invention uses the rotary gas phase thin film growing apparatus and the CVD method to grow a thin film on the silicon semiconductor substrate under a specific film-growing condition that is to say, using monosilane as an effective component of the material gas, causing the material gas to flow downward onto the surface of the silicon semiconductor substrate from above, controlling the number of rotation of the silicon semiconductor substrate in a range of 500 to 2000 minxe2x88x921 while operating under a reduced pressure of 2.7xc3x97102 to 6.7xc3x97103 Pa and causing a reaction in a temperature range of 600xc2x0 C. to 800xc2x0 C.
Thereby, an occurrence of a slip dislocation on the silicon semiconductor substrate can be restrained and more particularly, the occurrence of slip dislocation on the silicon semiconductor substrate having a diameter of as large as 300 mm or more can be restrained, which was conventionally considered difficult.
Moreover, a film growth rate is 0.01 to 0.5 xcexcm/min which indicates that it is possible to grow the high or equal quality thin film of uniform thickness without a rapid decrease of a film-growth rate as compared to that of the conventional method.
Furthermore, it is observed that the insulating pressure resistance characteristic of an oxide film obtained by oxidizing the grown thin film has an inside film characteristic of equal to or slightly higher than the thin film formed by a conventional method. Particularly, the method of chemically growing a thin film in a gas phase employed in the present invention is desirable for a method to grow a single crystal thin film such as a silicon epitaxial single crystal layer or the like on the silicon semiconductor substrate.